1. Field of the Invention
Exemplary aspects of the present invention relate to a development device and an image forming apparatus, and more particularly, to a development device for developing an electrostatic latent image into a toner image and an image forming apparatus including the development device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium (e.g., a sheet) according to image data using electrophotography. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner particles to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
For longer-lasting developer and faster image formation, the development device included in such image forming apparatuses may use a two-component developer containing non-magnetic toner particles and magnetic carrier particles. However, use of such two-component developer requires that the development device mix the toner particles and the carrier particles uniformly. Thus, for example, the development device may include an agitation member for agitating and mixing the toner particles and the carrier particles, or have a relatively long conveyance path to enable the developer to be agitated for a longer time period.
The development device typically includes a development roller, a first developer conveying screw, and a second developer conveying screw. The first developer conveying screw is disposed close to the development roller, and the second developer conveying screw is disposed near a toner inlet. With such a structure, new toner particles supplied to the development device through the toner inlet are agitated and mixed with existing toner particles and carrier particles already circulating within the development device, so that the toner particles and the carrier particles are mixed uniformly and circulated between the first developer conveying screw and the second developer conveying screw. The developer carried on the first developer conveying screw is then sent to the development roller so that a magnet in the development roller can form the developer into a magnetic brush on the surface of the development roller. When the brush of developer sweeps over a photoconductor disposed opposite the development roller, toner particles on the brush are attracted to an electrostatic latent image formed on the photoconductor by a development bias to make the electrostatic latent image visible as a toner image.
In such development device, it is necessary that the toner particles and the carrier particles be mixed uniformly to disperse the toner particles throughout the developer uniformly. Otherwise, insufficiently dispersed toner particles may spread uncontrolled over a recording medium bearing a toner image, staining a background of the toner image.
To address this problem, the development device may include a developer conveying screw having a screw-like flange or wing shape and a mesh screen mounted on the developer conveying screw. With such a structure, when the developer conveying screw rotates, a developer conveyed by the developer conveying screw passes through the mesh screen multiple times and the developer can be agitated efficiently.
Although such a development device provides improved agitation performance, the developer is subjected to greater mechanical stress, resulting in a shortened life of the developer.
Alternatively, the development device may include a developer collection path, a developer supply path, and a developer agitation path, each separated from the others by a partition plate or a partition wall, with each of the developer collection path, the developer supply path, and the developer agitation path provided with a screw for agitating and conveying a developer. With such a structure, a developer not used for developing an electrostatic latent image is collected into the developer collection path, and sent to the developer agitation path through the developer supply path. The developer is agitated in the developer agitation path and re-supplied to the developer supply path so that the developer is sent to a development roller to develop a next electrostatic latent image.
However, a complex structure is needed to control the three screws provided in the developer collection path, the developer supply path, and the developer agitation path, respectively, resulting in complicated control operations and increased manufacturing costs. This approach does not provide a simple, inexpensive way to achieve uniform mixing of the toner particles and the carrier particles.